The Influence of Modelling in Predictions of Vortex Interactions About a Generic Missile Airframe: RANS

Within the framework of the NATO Science and Technology Organization Applied Vehicle Technology Task Group AVT316 calculations have been made of the supersonic flow around a slender body with wings and fins. In this paper a synthesis of the results obtained using the Reynolds Averaged Navier-Stokes equations are presented. The results show significant sensitivity to the choice of turbulence model. Whilst the gross features of the flow are similar, details of the development of the leeward wake are different. Simple linear eddy viscosity models predict vortices that rapidly decay, resulting in weak interactions with the downstream fins and relatively small rolling moments. This is attributed to an over production in turbulence quantities that results in excessive effective turbulent viscosity. Interventions that limit the production of turbulence, for example the SST limiter or curvature corrections, results in vortices that grow more slowly, changing the nature of the downstream interactions resulting in increased rolling moment. The use of more complex formulations, such as Reynolds stress models, that are inherently more capable for highly strained flows, further limits the rate of growth of the vortex cores leading to rolling moment predictions that are 2-3 times greater than those obtained with the simples

The Influence of Scale Resolving Simulations in Predictions of Vortex Interaction about a Generic Missile Airframe

Hybrid Reynolds Average Navier-Stokes (RANS) - Large Eddy Simulations (LES) have been applied to predict the rolling moment coefficient of a generic missile at high angle of incidence in supersonic flow. The missile airframe was rolled which generated unsymmetrical vortices affecting the downstream tail fin section. Traditional RANS indicated difficulties predicting the rolling moment. This challenge was accepted by the NATO Science and Technology Organization (STO), Applied Vehicle Technology (AVT) panel forming a devoted Task Group AVT-316 “Vortex Interaction Effects Relevant To Military Air Vehicle Performance”. The paper describes the Missile Facets work on scale resolving simulations with spatial and temporal resolution strategy, quality index for LES and comparison with industry standard RANS methods. The hybrid RANS-LES results provided additional insights into the nature of the complex vortex interactions, including shocks, associated with slender body aerodynamics not detected with RANS. Scale resolving simulations drastically reduced vortex dissipation and resulted in significant shift of rolling moment magnitude

The Influence of the Numerical Scheme in Predictions of Vortex Interaction about a Generic Missile Airframe

Vortex dominated flows provide a challenge for modern computational fluid dynamics (CFD) solvers to accurately predict and capture the true physics of the flow. Modeling the formation and propagation of vortices downstream, as well as interactions with other vortices and shocks, are affected by a number of decisions including but not limited to the mesh generated, numerical scheme employed, and modelling assumptions. A research program has been underway for four years to study vortex interaction aerodynamics that are relevant to military air vehicle performance. The program has been conducted under the auspices of the NATO Science and Technology Organization (STO), Applied Vehicle Technology (AVT) panel by a Task Group with the identification of AVT-316. The paper at hand will look at the OTC1 test case [1], which is comprised of a generic missile configuration in supersonic flow, and the influence of the numerical scheme on the predicted results. The decision of the spatial discretization scheme, order of the turbulent flux, and choice of limiter were all shown to have strong influence on the predicted rolling moment of the OTC1 test case

Comparisons of Predicted and Measured Aerodynamic Characteristics of the DLR LK6E2 Missile Airframe

In this study, the influence of the turbulence model, grid resolution and flow solvers on the results of RANS simulations is investigated. The work is part of the NATO AVT Task Group AVT-316 (Vortex Interaction Effects Relevant to Military Air Vehicle Performance). Simulations have been carried out for a generic transonic missile configuration by various organizations and compared with data from wind tunnel experiments for a Mach number of M = 0.85, a roll angle of $\boldsymbol{45^\circ}$ and total incidences in the range of $\boldsymbol{15^\circ\leq\sigma\leq17.5^\circ}$. In the first part of the study each organization used their own computational mesh and best practice for the grid generation. In the second part a common mesh family (three grids) were used for the simulations. It was shown that even for the common mesh family, the results of the different flow solvers in some cases showed large variations. This applies in particular to the rolling moment. Here, the accurate flow solver-dependent prediction of the complicated flow topology on the large wings and the accurate prediction of the location of the leeward vortices have a particularly strong effect. Only one flow solver predicted this flow in a form that gave good agreement with the wind tunnel results over the entire investigated angular range

Comparisons of Predicted and Measured Aerodynamic Characteristics of the DLR LK6E2 Missile Airframe (Scale Resolving)

Time-accurate, turbulence scale resolving simulations of a transonic missile at high incidence and roll angle were performed and compared to simulations using standard Reynolds-Averaged Navier-Stokes turbulence models. The scale resolving simulations showed improved prediction of the total roll moment observed in wind tunnel tests compared to the RANS simulations, but still did not accurately predict the trend in roll moment with incidence angle in the range 15.0°≤σ≤17.5°. The scale resolving simulations predicted less turbulence energy in the vortex structures and larger separation regions over the wings. Spectral analysis of the roll moment signal showed dominant frequency modes consistent with a leading-edge vortex breakdown over two wings

The Influence of Modelling in Predictions of Vortex Interactions About a Generic Missile Airframe: RANS

Within the framework of the NATO Science and Technology Organization Applied Vehicle Technology Task Group AVT316 calculations have been made of the supersonic flow around a slender body with wings and fins. In this paper a synthesis of the results obtained using the Reynolds Averaged Navier-Stokes equations are presented. The results show significant sensitivity to the choice of turbulence model. Whilst the gross features of the flow are similar, details of the development of the leeward wake are different. Simple linear eddy viscosity models predict vortices that rapidly decay, resulting in weak interactions with the downstream fins and relatively small rolling moments. This is attributed to an over production in turbulence quantities that results in excessive effective turbulent viscosity. Interventions that limit the production of turbulence, for example the SST limiter or curvature corrections, results in vortices that grow more slowly, changing the nature of the downstream interactions resulting in increased rolling moment. The use of more complex formulations, such as Reynolds stress models, that are inherently more capable for highly strained flows, further limits the rate of growth of the vortex cores leading to rolling moment predictions that are 2-3 times greater than those obtained with the simplest models